Specimen description :

• Almost complete trilobite.
• Enrolled on matrix
• Small granulations on the exosqueletton.
• Total size : 26 x 12 mm
• middle-upper Ordovician
• Cobourg Formation.
• Ontario, Canada

Order

Phacopida

SALTER 1864

Occurrence: Lower Ordovician (Tremadoc) to Upper Devonian (Famennian).

• Cephalon: Proparian (Phacopina and Cheirurina), gonatoparian (Calymenina) or opisthoparian (Calymenina),
• Preglabellar field often very short or absent.
• 4 or fewer pairs of glabellar furrows.
• Eyes : when present, schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina).
• With rostral plates (Calymenina and Cheirurina) or without (some Phacopina).
• Hypostome conterminant (all suborders) to impendent (some devonian Phacopina).
• Exosqueletton generally granulous.
• Thorax: 8 – 19 segments, sometimes distinctly furrowed.
• Axis sometimes broad (e.g., Homalonotidae).
• Pygidium : Typically micropygous (most Calymenina and Phacopina), but variable (e.g., subisopygous in Dalmanitoidea and Acastoidea).
• May be lobed or spiny (e.g., Cheirurina, some Dalmanitoidea, Acastoidea), or smooth-margined, with round or subtriangular outline (e.g., Calymenina, Phacopoidea).

Sub-order

Cherirurina

HARRINGTON & LEANZA 1957

• Cephalon: proparian sutures (a few opisthoparian).
• Glabella usually expanding forwards or barrel-shaped, up to 4 pairs of furrows;.
• Holochroal eyes, often small.
• Gena often with fine pitting.
• With rostral plate.
• Hypostome conterminant, with anterior wing bearing prominent process.
  Thorax: variable numbers of distinctive segments within Phacopid range of 8-19.
• Often spine-tipped.
  Pygidium: often highly modified with 2-16 distinct pairs of ribs.
• Lobed or spinose margin.
  Other: often with tuberculate exoskeleton.

Family

Cheiruridae

HAWLE & CORDA 1847

• Thorax : Pleurae with pointed or rounded spines.
• Oblique or transverse pleural furrows (in some genera represented by pits, or effaced).
• Pygidium : 2 to 4 pairs of pleural ribs and spines.
• Axial rings few.
• Other : surface commonly tuberculate, pitted or both.

Sub-family

Cheirurinae

HAWLE & CORDA 1847

• Cephalon : Glabella expanding forward or with subparallel sides.
• Preoccipital lateral glabelar furrows generally curved backward, commonly joining occipital furrow.
• Hypostoma with elongate middle body.
• Thorax : generally of 11 segments.
• Proximal part of pleurae with distinct oblique pleural furrows.
• Pygidium : with 2 or 3 pairs of pleural spines.
• 2 posterior pairs more or less reduced in some.

Genus

Leviceraurus

HESSIN 1988

• Cephalon : moderatly inflated and nearly parallel-sided glabella.
• 3 pairs of short glabellar furrows.
• Width across occipital ring slightly less than one-fourth width of cephalon.
• Occipital ring broad, about one-fourth length of glabella.
• Glabella smooth to unaided eyes, but has prosopon of very fine granules and typically four pairs of low, rounded tubercles on medial portion of glabella (often fourth pair and one third pair absent).
• Eye small, elevated and positionned on mid-point of cheek opposite 2S furrow or 2p lobe.
• Rostral plate possessing a pair of faint tubercles.
• Anterior border very narrow, almost indistinguishable from anterior lobe of glabella.
• Genal spines moderately long, extanding back to opposite 4th or 5th thoracic segment.
• Pygidium : Triangular in outline.
• Excluding slender anterior spines which are almost as long as length of thorax.
• 2 pairs of posterior spines present but very short.

Species

mammilloides

HESSIN 1988

• As for genus.